1. Field of the Invention
The present invention relates to an electro-acoustic transducer such as a speaker and a microphone.
2. Description of the Related Art
As a known example of an electro-acoustic transducer similar to a constitution of the present invention in which one vibration part is disposed between two stator parts, there is one in which an attractive force owing to an electrostatic force acts between the vibration part and the stator parts to perform electro-acoustic conversion operation by the change of the attractive force and the vibration change of the vibration part in response to the change of the attractive force.
For example, in an electrostatic electro-acoustic transducer shown in a frame format of FIG. 3, a film-shaped vibration pole 10 capable of performing vibration displacement is disposed in parallel between two stator poles 20 disposed in parallel with each other. The vibration pole 10 is charged to one polarity (plus in shown example) and the stator poles 20 are charged to the other polarity (minus in shown example) to generate an electrostatic attractive force between the vibration pole 10 and the stator poles 20. The potential of the stator pole 20 is changed by an acoustic signal unit 30 connected to the stator pole 20 to generate change of the attractive force and drive the vibration pole 10, thereby generating acoustic wave. If the vibration pole 10 is vibrationally displaced by the generated acoustic wave or acoustic wave from outside, electric charge moves or acoustic signal current flows between the vibration pole 10 and the stator pole 20 by electrostatic induction and by way of detection thereof the electro-acoustic conversion is performed. This constitution is disclosed in Japanese Unexamined Patent Application Publication No. 56-165490.
However, in the above-described related art that is operated by causing an electrostatic attractive force between the vibration pole and the stator pole, since the intensity of an attractive force acting between the vibration pole and the stator pole is increased with inversely proportional to square of a distance between the vibration pole and the stator pole, there may be a serious problem that the vibration pole contacts with the stator pole. In order to cope with the problem, the constitution of the electro-acoustic transducer becomes complicate, and amplitude is limited. Moreover, deformation and noise are generated.
Since an attractive force acts between the vibration pole and the stator pole, in order to position the vibration pole in place with respect to the stator pole, it is necessary to mechanically fix and maintain the vibration pole in a state that the vibration pole is tensioned by an elastic restorative force. Accordingly, the structure becomes complicate and the selection of material is limited for obtaining proper elasticity.
Since the vibration pole must vibrationally displace in a state that the vibration pole is mechanically fixed and maintained, the operation of vibration displacement becomes elastic deformation displacement and deterioration with age may easily caused by elastic fatigue.
Moreover, it is not known that a vibration part is disposed between two stator parts and a repulsive force is caused between the stator part and the vibration part by a magnetic force to perform operation for electro-acoustic conversion by the change of the repulsive force by magnetic force and the vibration change of the vibration part in response to the change of the repulsive force.